To obtain a better understanding of the olfactory processes that allow mosquitoes to identify human hosts, a comprehensive molecular study will be performed to identify and characterize molecules in the olfactory signaling pathway of the African malaria vector Anopheles gambiae. Using cDNA libraries from antennae of females and males, a collection of cDNAs encoding odorant binding proteins (OBPs) and other antennal proteins has already been isolated and characterized. Using a micro-array and quantitative RT PCR techniques, regulation of expression of these genes in antennae will be investigated, and spatial distribution of transcripts and proteins will be studied. Concentrating on chemicals that have previously been shown to be attractants for female mosquitoes and also elicit an electrophysiological response, in vitro binding assays will be performed to study the interaction of specific odor molecules with mosquito OBP proteins and to identify their natural ligands. To investigate whether altered expression of specific OBPs in antennae causes detectable behavioral and electrophysiological changes, mosquitoes will be generated in which the expression of specific OBPs is reduced by the expression of double-stranded RNA (RNAi) from transgenes. Suppression of OBP expression will be monitored by RT PCR. The modified mosquitoes will be tested in wind tunnel experiments for behavioral changes in response to odorants, and for electrophysiological changes by single sensilla recordings. These studies will ultimately allow the development of better methods to interfere with the mosquito-host interaction and reduce transmission of the malaria parasite.